Folding Propeller for a Water Vehicle

ABSTRACT

The present disclosure relates to a folding propeller ( 10 ) for a water vehicle, comprising a hub ( 12 ) which is drivable about a rotation axis (D) via a drive shaft, and a propeller blade ( 14 ) which is arranged on the hub ( 12 ) to be pivotable about a pivot axis (S) between a maximum closed position (P 1 ) and a maximum open position (P 2 ), wherein the pivot axis (S) defines, together with a normal (N D ) to the rotation axis (D) which intersects the pivot axis (S), a maximum opening plane (E Max ), wherein in the driven state and a pivot position of the propeller blade ( 14 ) in the region of the maximum open position (P 2 ), at least one opening force acts upon the propeller blade ( 14 ) which results from rotation of the folding propeller ( 10 ) and in relation to the rotation axis (D) is directed substantially radially outwardly, wherein an effective force application point (EAP) of the opening force is arranged spaced from the maximum opening plane (E Max ) and is substantially arranged in the closing direction (SR) of the propeller blade ( 14 ). The present disclosure further relates to a folding propeller ( 10 ) comprising a propeller blade ( 14 ) which has a reversal element ( 143 ) which is configured such that during rearward drive a reversed thrust (F reverse ) acts upon the reversal element ( 143 ) and is directed substantially perpendicularly to the propeller blade longitudinal axis (L P ) in the opening direction (OR) of the propeller blade ( 14 ).

RELATED APPLICATION(S)

This application claims priority to and the benefit of German Patent Application No. DE 10 2021 102 842.6, filed on Feb. 8, 2021, the contents of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a folding propeller for a water vehicle, in particular, for a sailing boat, and a drive for a water vehicle with such a folding propeller.

BACKGROUND

Folding propellers for use in water vehicles, for example, as a drive in sailing boats, are known. Boats can have a drive that is equipped with a folding propeller in order, in certain situations with an opened, driven folding propeller to generate a desired forward propulsion, whereas in other situations, with a closed non-driven folding propeller, these boats benefit from a relatively low water resistance.

In the case of a folding propeller, the possibility exists of opening and closing the propeller blades, particularly by means of its design configuration: typically, two or more propeller blades are mounted to be pivotable about respective pivot axes arranged in a propeller hub and are thereby connected to said hub. The propeller hub is driven by means of a drive shaft and the pivot axes lie perpendicularly to the rotation axis of the propeller hub. By means of this arrangement, during rotation of the propeller hub, centrifugal forces act upon the propeller blades. These centrifugal forces cause an opening of the propeller blades.

Typically, a folding propeller is configured as a pusher propeller and is arranged in the central region or at the stern of the boat.

In general, a driven propeller accelerates the surrounding water against the direction of travel, so that its propeller blades undergo a thrust in the direction of travel. This thrust in the direction of travel is transmitted by the propeller blades to the propeller hub and thus via the drive to the boat.

In the case of a folding propeller, such a thrust of the accelerated surrounding water on the propeller blades during forward travel supports the pivoting motion of the propeller blades in the opening direction. During rearward travel, by contrast, such a thrust acts closingly upon the propeller blades, i.e. it possibly causes a pivot movement of the propeller blades in the closing direction. In other words, during rearward travel, the propeller blades accelerate the surrounding water substantially in the direction of the bow of the boat, so that the resulting thrust is applied to the propeller blades and is directed in a rearward travel direction. This promotes a possible pivot movement of the propeller blades in the closing direction, although the centrifugal forces applied to the propeller blades counteract this closing pivot movement. In practice it is observed that during rearward travel, a middle open position of the propeller blades in which the openingly acting centrifugal forces and the closingly acting thrust-related forces substantially cancel each other out. The resulting middle open position of the propeller blades leads to significant losses in relation to forward propulsion and the maneuverability of the boat.

For braking during forward travel, the disadvantages of rearward travel described above apply correspondingly. A complicating factor is the prevailing movement flow which additionally presses the propeller blades in the closing direction.

In order to counteract the problems described, for conventional folding propellers, it is known in the case of rearward travel to increase the centrifugal force by increasing the rotary speed in order to open the propeller blades further from a middle open position. With regard to the structural design, it is known to increase the mass of the propeller blades of folding propellers in order to increase the desired centrifugal force.

Propeller blades of folding propellers are typically made of metal having high density values. Standard materials are, for example, brass alloys or stainless cast steel with typical densities of 7800 to 8900 kg/m³. The propeller blades are typically made by casting and spur gear toothing responsible for the synchronization of the propeller blades is made by machining. With this material selection, the complete folding propeller becomes very heavy and the forces arising during operation become very large. This can, in turn, negatively affect the rest of the drive system. For example, the heavy propeller blades can generate unwanted vibrations and sounds. In addition, severe jolts can be caused during opening of the propeller blades, due to the large masses being moved. Furthermore, the production is complex and the total weight of the boat is increased. It is also disadvantageous that the alloys used either themselves corrode or have a corrosive effect on other metal components of the boat. For this reason, galvanic anodes which are to be regarded as expendable parts are needed, so that the servicing costs increase.

SUMMARY

Proceeding from the known prior art, it is an object of the present disclosure to provide an improved folding propeller for a water vehicle, for example a boat, in particular a sailing boat.

The object is achieved with a folding propeller having the features of the independent claims. Advantageous developments are disclosed in the subclaims, the description and the drawings.

Accordingly, a folding propeller for a water vehicle is proposed which comprises a hub that is drivable about a rotation axis by means of a drive shaft. The folding propeller also comprises at least one propeller blade which is arranged on the hub to be pivotable about a pivot axis between a maximum closed position and a maximum open position. The pivot axis therein defines, together with a normal to the rotation axis that intersects the pivot axis, a maximum opening plane. If, in the driven state, the propeller blade is in the maximum open position, then an opening force acts upon the propeller blade, said force resulting from the rotation of the folding propeller and being directed substantially radially outwardly in relation to the rotation axis. The folding propeller is configured in such a way that an effective force application point of the opening force is spaced from the maximum opening plane and is arranged substantially in the closing direction of the propeller blade.

In other words, the effective force application point is always arranged, relative to the bow of the boat, behind the maximum opening plane, so that particularly in a pivot position of the propeller blade in the region of the maximum open position, an opening force can be constantly applied to the effective force application point, said force generating via a lever to the pivot axis, a moment acting with an opening effect on the propeller blade.

An effective force application point should be understood in the context of the present disclosure to be an imaginary or actual application point or application region of a physical and/or mechanical force that is suitable for representing the corresponding force application and for making it usable for other considerations. This is helpful, in particular, if for example a local force variation (for example, in the case of uplift) or a volume force (for example, in the case of centrifugal force) exists and is to be used for defining a moment.

Furthermore, in the context of this disclosure, it is the case that where reference is made to a propeller blade or a propeller blade is described, this can apply to a plurality of, and in particular all, propeller blades, which includes the folding propeller. The folding propeller can comprise two, three, four or more propeller blades.

The maximum closed position results when the propeller blade is pivoted such that its longitudinal axis extends substantially parallel to the rotation axis. Alternatively, this pivot position can also be referred to as a folded-in position of the propeller blade. This occurs, in particular, if the folding propeller is not powered, that is, if the hub is not driven by the drive, for example if the boat is operated in sail mode and accordingly a water flow acts in the closing direction of the propeller blade.

Accordingly, a pivot movement of the propeller blade about the pivot axis toward the maximum closed position is herein described as “closing” or “in the closing direction”, whereas a pivot movement directly contrary thereto is described as “opening” or “in the opening direction”. This applies accordingly for forces and moments that can act upon the propeller blade.

The maximum open position results when the propeller blade is pivoted so that, due to its arrangement in the folding propeller, it can no longer carry out any further pivot movement in the opening direction. Alternatively, this can be referred to as an unfolded position of the propeller blade or the folding propeller.

The paired terms open/closed position, open/close, maximum open/closed position relate to the propeller blade but can relate with equal validity to the entire folding propeller. This applies, in particular, if the propeller blades arranged in the folding propeller are pivot-synchronized, which can take place via a synchronizing apparatus in the root region of the respective propeller blades.

The effective force application point of the opening force may correspond to the center of mass of the propeller blade. In this case, the at least one opening force is a centrifugal force.

Additionally, or alternatively, the effective force application point of the opening force may correspond to the center of pressure of an additional body arranged on the propeller blade. This additional body can be configured as an uplift body generating uplift, for example, in the form of a winglet generating an uplift. In this case, the at least one opening force is an uplift force.

The centrifugal force and the uplift force have in common that they each are applied to an effective force application point which is arranged on the propeller blade and is spaced in the closing direction relative to the maximum opening plane, and that they can generate, via a lever, an opening moment about the pivot axis. This opening moment is suitable for pivoting the propeller blade in the opening direction or for counteracting forces or moments acting closingly on the propeller blade.

For this purpose, firstly the centrifugal force and later the uplift force are considered below.

In the driven state, a centrifugal force acting upon the center of mass can be applied to the propeller blade which can essentially be dependent upon:

the current rotary speed, that is, the current angular speed of the hub; and/or

the mass and mass distribution of the propeller blade, in other words, the absolute value of mass and the position of the center of mass within the propeller blade; and/or

the current relevant radius, in other words, the current radial spacing of the center of mass of the propeller blade from the rotation axis.

The propeller blade may have a center of mass which is arranged such that in the maximum open position of the propeller blade, it is spaced in the closing direction from an imaginary maximum opening plane. In other words, the center of mass of the propeller blade (referred to hereinafter simply as “center of mass”) in the maximum open position of the propeller blade has an offset in the closing direction relative to the maximum opening plane.

The maximum opening plane is imagined to be defined by the pivot axis and that normal to the rotation axis which crosses the pivot axis. Alternatively, the maximum opening plane can be imagined as being the plane in which the pivot axis lies and the normal of which is directed parallel to the rotation axis.

The offset of the center of mass as described above can have the effect in the arrangement described that the centrifugal force acting on the propeller blade due to the rotation of the folding propeller which is applied, in a simplified consideration, to the center of mass always has a centrifugal force component that is directed perpendicularly to a lever about the pivot axis and thus causes an opening moment. This applies, in particular, in the maximum open position of the propeller blade.

In the arrangement of the center of mass, account can be taken thereof that in the maximum closed position, it may also have a further offset, specifically an offset in relation to the rotation axis in the opening direction. In other words, in the maximum closed position, the center of mass does not pass beyond the rotation axis that is of decisive importance for the centrifugal force. This further offset can ensure that with the start of a rotary movement of the hub even from a standstill, an opening centrifugal force can operate upon the propeller blade, that is it can be applied over the current centrifugal force radius to the center of mass and can act in the opening direction.

In one embodiment, the maximum open position may be defined by means of a stop apparatus of the folding propeller. In other words, in the maximum open position, a first element of the stop apparatus, which may be arranged on the propeller blade, is in contact with a second element of the stop apparatus, which may be arranged on the hub. Thus, the stop apparatus can ensure that the propeller blade can carry out no further pivot movement in the opening direction, so that the center of mass can remain always offset in the closing direction from the maximum opening plane. Furthermore, the stop apparatus may comprise further means which enables, for example, an adjustment thereof and/or by means of which a damping may be set up. Damping elements can be used therein to damp the impulse of the impact of the propeller blade against the hub and/or to hold the propeller blade better in the maximum open position in a possibly prevailing dynamic equilibrium.

In a further embodiment, the propeller blade may have a first propeller blade portion and a second propeller blade portion, wherein the first propeller blade portion is arranged distally and the second propeller blade portion is arranged proximally in relation to the pivot axis along the propeller blade longitudinal axis. In other words, the first, distal propeller blade portion along the propeller blade longitudinal axis has a greater spacing from the rotation axis than the second, proximal propeller blade portion.

In this regard, proximal herein characterizes a direction or arrangement that faces or lies along the propeller blade longitudinal axis substantially toward the pivot axis. Similarly henceforth, distally characterizes a direction or arrangement that faces or lies along the propeller blade longitudinal axis substantially toward the propeller blade tip.

According to one embodiment, the first propeller portion may be offset relative to the second propeller blade portion substantially in the closing direction. This arrangement can enable or favor the offset of the center of mass in the maximum open position of the propeller blade relative to the maximum opening plane in the closing direction and can positively influence it in the context of the opening moment.

In a further embodiment, the propeller blade may have a propeller blade tip portion, a propeller blade shaft portion and a propeller root portion, wherein the propeller blade tip portion is arranged distally, the propeller blade root portion is arranged proximally and the propeller blade shaft portion is arranged therebetween. The propeller blade shaft portion and/or the propeller blade tip portion may be offset substantially in the closing direction in relation to the propeller blade longitudinal axis relative to the propeller blade root portion. In other words, the propeller blade tip portion alone or the propeller blade tip portion together with the propeller blade shaft portion may form the first, distal propeller blade portion. Accordingly, the propeller blade root portion alone or the propeller blade root portion together with the propeller blade shaft portion may form the second, proximal propeller blade portion.

According to a further embodiment, different propeller blade portions may have different geometries and material densities. By means of the arrangement of the different propeller blade portions relative to one another, the arrangement of the center of mass—and, in general, the effective force application points—can thus be influenced to affect the opening moment.

In addition, such a multi-part embodiment of the propeller blade is advantageous since different propeller blade configurations can be produced by simple means in that, for example, different embodiments of propeller blade tip portions and propeller blade shaft portions can be assembled with regard to significant parameters such as geometry, mass or material, in a modular manner. Thus, by simple means, different propeller blades can be produced with differently arranged centers of mass or effective force application points for different folding propellers.

Furthermore, the propeller blade may be designed such that the center of mass is arranged distally in relation to the centroid of the propeller blade and is located, for example, in the propeller blade tip portion or in the propeller blade shaft portion. In other words, the first, distal propeller blade portion may have a greater material density than the second, proximal propeller blade portion. In this way, a particularly advantageous centrifugal force acting upon the propeller blade can be enabled, in particular if this centrifugal force is considered in relation to the mass of the propeller blade and thus to the inertia of the folding propeller. This means that through the possibilities for the arrangement of the center of mass, firstly the centrifugal force behavior of the propeller blade can be optimized while, simultaneously, secondly the mass and thus the inertia of the propeller blade can be improved in the design configuration.

In some embodiments, the propeller blade may have a propeller root, whereby the propeller root has a mounting apparatus for attaching the propeller blade to the hub and the mounting apparatus defines the pivot axis which in some embodiments extends perpendicularly to the rotation axis.

In a further embodiment, the propeller blade tip portion can be formed of metal. This enables an advantageous mass distribution within the propeller blade and, in particular, the center of mass can be influenced and the inertia of the propeller blade can be optimized.

In a further embodiment, the propeller blade tip portion may have an additional body which can form a propeller blade tip. The additional body may be configured as an uplift body and/or as a mass body. The uplift body is in some embodiments configured as a winglet generating an uplift, whereas the mass body in some embodiments has a mass element, for example, in the form of a curved cylinder. The configuration of the additional body as a mass body advantageously enables further influencing of the arrangement of the center of mass. The advantages of an embodiment of the additional body as an uplift body is described further below. In addition, an advantageous embodiment of the additional body is possible wherein the additional body is designed both as an uplift body and also as a mass body and therefore has the respective advantages together.

Therein, the propeller blade or the propeller blade tip portion may be configured integrally with the additional body. This can enable a stiff and/or flow-optimized attachment of the additional body.

In a further embodiment, the propeller blade tip portion may be connected form-fittingly or frictionally to the propeller blade shaft portion. For example, the propeller blade tip portion may have a tongue which may be cast into the propeller blade shaft portion and/or is connected to the propeller blade shaft portion via a releasable connection, in particular, a screw connection. Alternatively, the propeller blade shaft portion may be connected via a rivet connection or a bonded connection to the propeller blade shaft portion.

This advantageously enables both a modular construction and also a composite construction of the propeller blade, since the components of the propeller blade portion can be formed differently and can have different materials. In the case of a releasable connection or a rivet connection, there are further advantages with regard to repair, servicing or replacement of the propeller blade tip portion.

In a further embodiment, a metal inlay may be embedded in the propeller blade. Therein, the propeller blade or propeller blade portions can be made of plastics. In some embodiments, the metal inlay is molded in with a plastics injection molding method. In other words, the propeller blade can be enclosed in plastics. With a composite design of this type, the folding propeller can be configured to be resistant to corrosion and at the same time, the propeller blade can be improved with regard to the arrangement of the center of mass with regard to the offset described above to affect the opening moment and its inertia.

According to a further embodiment, the hub may be formed of plastics. This reduces the moment of inertia of the hub and the hub can be formed with a larger diameter. Thus, the spacing of the mounting apparatus, and thus of the pivot axis, from the rotation axis can be increased as compared with conventional folding propellers. In this way, the radial spacing of the center of mass from the rotation axis can be increased, which can have an advantageous effect on the opening centrifugal force component. In addition, said spacing increase enables more degrees of freedom for the design of the propeller blade, in particular, with regard to the additional body and/or the propeller blade tip portion. This enables an improved geometrical integration within the folding propeller arrangement, in particular, with regard to the maximum closed position, where undesirable interference of the propeller blades and, in particular, their propeller blade tip portions or additional bodies shall not occur.

The uplift force, as mentioned elsewhere, which can act as an opening force and can contribute to the creation of the opening moment is considered below.

As described above, the uplift body may be configured in the form of a winglet. In this regard, a winglet is to be understood as an element which, due to its profile of, for example, an airfoil profile and/or due to its arrangement, for example, an inclination, pitch or torsion relative to the remainder of the propeller blade, experiences a dynamic uplift when surrounding water flows over it. This can be referred to as a “functional winglet”.

In particular, the uplift force acting upon the uplift body may include an openingly acting uplift force component, which acts on the propeller blade to provide the opening moment. For simplification and improved legibility of the description, the winglet is primarily described below, although the description equally applies, in general, for the uplift body according to the present disclosure.

The openingly acting uplift force component acts upon the center of pressure of the winglet and is oriented perpendicularly to a lever which corresponds to the radial distance from the pivot axis to the center of pressure of the winglet taking account of the angle of action of the uplift force vector of the winglet. In the context of this disclosure, the center of pressure is to be understood to be the effective force application point of the uplift force on the winglet. The position of the center of pressure and the direction of the uplift force vector depends, inter alia, on the profile and arrangement of the winglet. For example, the center of pressure may be arranged at the intersection point of a winglet uplift force vector and the winglet chord.

According to one embodiment, the winglet may be configured so that in the driven state of the folding propeller, such an openingly acting uplift force component engages upon the winglet in each pivot position of the propeller blade, said force component acting via a lever in the rotary direction of the opening moment. In particular, this is the case when the propeller blade lies in the maximum open position or in a position which lies in the region of, or close to, the maximum open position.

According to one embodiment, the dynamic uplift force that acts upon the winglet may be generated and/or favored in the following way: The winglet may have a cross-section which substantially corresponds to an airfoil which generates uplift when a suitable medium flows round it. The flow required for the uplift can take place through the relative movement of the winglet with respect to the surrounding water. In particular, the aforementioned flow can be caused by the rotation of the folding propeller, in other words, by the circular movement of the winglet about the rotation axis.

Therefore, in the driven state a dynamic uplift force can act upon the winglet, said force being substantially dependent, with regard to endogenous parameters, upon:

the rotary speed of the folding propeller, that is a current velocity of travel of the winglet about the rotation axis; and/or

a longitudinal inclination of the winglet, that is for example, an inclination angle between the winglet longitudinal axis and the propeller longitudinal axis or the longitudinal axis of the second propeller blade portion; and/or

the winglet cross-section, for example, an airfoil profile of the winglet, designated the winglet profile below; and/or

an angle of incidence between a winglet chord and that flow against the winglet which is substantially directed tangentially to the propeller blade periphery.

The winglet chord should be understood, similarly to an airfoil chord, to be the imaginary connecting line between a winglet front edge and a winglet rear edge. The winglet profile may be configured so that the openingly acting uplift force component is generated for both possible rotary directions of the folding propeller. Accordingly, during forward drive, the winglet front edge corresponds to a leading edge and during rearward drive, the winglet rear edge corresponds to the leading edge.

A person skilled in the art will appreciate that in the case, for example, of a required design trade-off, the embodiment of the winglet profile in which a greater dynamic uplift is generated during rearward travel than during forward travel (with otherwise comparable parameters) can be advantageous. It can be required, in particular, that the openingly acting uplift force component during rearward travel advantageously contributes to the opening moment since particularly during rearward drive, a closing moment can act upon the propeller blade.

Furthermore, the winglet may be configured, for example, by means of the winglet shape, the winglet inclination and/or the attachment to the propeller blade such that in an opened position, the movement flow of the surrounding water exerts an opening force on the winglet.

In particular, a person skilled in the art will recognize that the desired openingly acting uplift force component of the winglet cannot be favorably influenced exclusively by means of one of the embodiments described above. For example, the winglet must not necessarily have an airfoil profile, but rather may also be formed, for example, via obliquely positioned plate elements which may have a planar, curved or other suitable shape.

Furthermore, advantageous embodiments may be included in which the propeller blade portions are arranged adjustable among one another or in which the additional body is arranged adjustable relative to a propeller blade portion. In such configurations, the opening moment can be adapted by optimizing the corresponding centrifugal force and/or the uplift force and, in particular, with respect to different operating parameters such as, for example, rotary speed, propeller blade pivot position, surrounding water flow. This optimization applies, in particular, with regard to the respectively resultant closing moment, which a person skilled in the art can ascertain during the designing of the folding propeller for different operating scenarios and parameters.

In some embodiments, the propeller blade has on an end side of the propeller blade root portion or the propeller blade root, a spur gear toothing, by means of which the propeller blade can mesh with other propeller blades of the folding propeller in order to synchronize the pivot movement of the propeller blades with one another. Therein the propeller blades may be arranged at even angular spacings surrounding the hub.

The object defined above is further achieved by means of a folding propeller having the features of independent claim 15. Advantageous developments are disclosed in the subclaims, the following description and the drawings.

Features of the folding propeller according to claim 15 can be used, in particular, in combination and/or additionally with the embodiments described above. Such combinations and/or additions can therefore be regarded as being disclosed.

Accordingly, a folding propeller for a water vehicle is proposed which comprises a hub that is drivable about a rotation axis by means of a drive shaft. The folding propeller also comprises a propeller blade which is arranged on the hub to be pivotable about a pivot axis. The propeller blade has a reversal element which is configured such that during rearward drive, a reversed force acts upon the reversal element which is oriented substantially perpendicularly to the propeller blade longitude axis in the opening direction of the propeller blade.

The attribute “reversed” in the expression “reversed force” denotes, in the context of the present disclosure, a direction which can be directed substantially contrary to the propeller blade uplift force primarily striven for to generate a resulting drive thrust. According to one embodiment, the reversal element is arranged in a propeller blade tip portion. This enables the advantageous elongation of a desired lever for the reversed force. This is relevant, in particular, with regard to an observation of moments acting openingly or closingly on the propeller blade during rearward drive.

According to a further embodiment, the reversal element is arranged on the propeller blade pivotable about a pivot axis which is substantially parallel to the propeller longitudinal axis. This can take place by means of a corresponding mounting apparatus.

In a development, the reversal element may be arranged on the propeller blade pivotable between a maximum folded-in position and a maximum folded-out position. The reversal element assumes the maximum folded-in position when the folding propeller is in forward drive. This can take place substantially automatically through the flow present during forward drive. Therein, the reversal element can be oriented, in the maximum folded-in position, substantially aligned with the propeller blade. This minimizes or reduces undesirable flow resistance in forward drive.

Furthermore, in this development, the reversal element assumes the maximum folded-out position when the folding propeller is in rearward drive. The reversal element may, in particular, be configured and arranged on the propeller blade so that the pivoting of the reversal element takes place in the direction of the maximum folded-out position substantially automatically due to the flow against the propeller blade edge accordingly present during rearward drive. The maximum folded-out position may be defined by design means or a suitable arrangement. For example, suitable stop elements may be arranged on the reversal element and/or on the propeller blade. In other words, the stop elements are configured to prevent the reversal element being pivoted beyond the maximum folded-out position. Furthermore, the stop elements and/or the mounting apparatus may be configured to transfer the flow forces acting upon the reversal element in rearward drive as reversed force from the reversal element to the propeller blade.

Furthermore, the reversed force can generate an openingly acting moment on the propeller blade via a lever to the pivot axis of the propeller blade.

Naturally, in the case of folding propellers during rearward drive, forces or moments acting openingly and closingly upon the propeller blade act against one another. Accordingly, the reversal element may be configured and connected to the propeller blade such that during rearward drive, the flow forces of the flow can be converted at the reversal element into the reversed force which engages upon an effective force application point and via the lever to the pivot axis of the propeller blade, generates an opening moment. In particular, this opening moment is suitable for preventing a pivot movement of the propeller blade in the closing direction or for holding the propeller blade in a region between a middle open position and a maximum open position.

Further advantages and features of the present disclosure are disclosed in the description below of exemplary embodiments. The features described therein can be implemented alone or in combination with one or more of the aforementioned features, provided the features do not contradict one another. The following description of preferred exemplary embodiments makes reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present disclosure are explained in detail below with the following description of the drawings. In the drawings:

FIG. 1 is a schematic partially sectional plan view of a folding propeller according to one embodiment;

FIG. 2a is a partially sectional plan view of a propeller blade of the folding propeller shown in FIG. 1 in a maximum closed position and in a middle open position;

FIG. 2b is a continuation of the view of FIG. 2 a;

FIG. 3a is a schematic front view of a folding propeller according to a further embodiment;

FIG. 3b is a schematic side view of a propeller blade tip portion of a propeller blade;

FIG. 3c is a schematic side view of a propeller blade tip portion of a propeller blade;

FIG. 3d is a schematic front view of a tongue of a propeller blade tip portion of the propeller blade shown in FIG. 3a according to one embodiment;

FIG. 3e is a schematic front view of a tongue of a propeller blade tip portion of the propeller blade shown in FIG. 3a according to a further embodiment;

FIG. 4 is a schematic front view of a folding propeller with a propeller blade having a metal inlay according to a further embodiment;

FIG. 5 is a schematic partially sectional plan view of a folding propeller with a winglet according to a further embodiment;

FIG. 6 is a schematic cross-sectional view of an embodiment of the winglet shown in FIG. 5;

FIG. 7 is a perspective view of an embodiment of the winglet shown in FIG. 5;

FIG. 8 is a perspective schematic view of a water vehicle during rearward drive with a folding propeller according to a further embodiment;

FIG. 9a is a schematic front view of the propeller blade shown in FIG. 8;

FIG. 9b is a schematic side view of the propeller blade shown in FIG. 9 a;

FIG. 10a is a schematic front view of the propeller blade shown in FIG. 8 during forward drive; and

FIG. 10b is a schematic side view of the propeller blade shown in FIG. 10a during forward drive.

DETAILED DESCRIPTION

Exemplary embodiments are described below making reference to the drawings. Herein, identical, similar or similarly acting elements are provided with the same reference signs in the different drawings, and repeated description of these elements is in part dispensed with for the avoidance of redundancy.

FIG. 1 shows a schematic partially sectional plan view of a folding propeller 10 according to a first embodiment. The folding propeller 10 comprises a hub 12 and two identical propeller blades 14.

In the text below, the present embodiments are illustrated for simplification on the basis of an individual propeller blade 14. For greater clarity, the reference signs in FIG. 1 are shown distributed over both propeller blades 14, although the two propeller blades 14 do not differ functionally or structurally.

The propeller blade 14 has a propeller root 15 which has a mounting apparatus 16 for attaching the propeller blade 14 to the hub 12. The hub 12 is rotatable about a rotation axis D and drivable via a boat drive shaft (not shown) to which it is connected for conjoint rotation. The mounting apparatus 16 defines a pivot axis S which is arranged perpendicularly to the rotation axis D. The propeller blade 14 is pivotable about the pivot axis S between a maximum closed position (P1, not shown) and a maximum open position P2. In the contact region of the propeller root 15 and the hub 12, the folding propeller 10 has a stop apparatus 18 which limits the opening of the propeller blade 14 and thus defines the maximum open position P2.

A normal N_(D) to the rotation axis D crossing the pivot axis S defines, together with the rotation axis D, a maximum opening plane E_(Max) of the propeller blade 14 or of the folding propeller 10. The maximum opening plane E_(Max) can arbitrarily but does not necessarily correspond to the maximum open position P2, since the latter is defined by the stop apparatus 18, whereas the maximum opening plane E_(Max) substantially depends upon the pivot axis. Rather, the maximum opening plane E_(Max) serves to define the arrangement of effective force application points, for example, the center of mass MSP of the propeller blade 14. The center of mass MSP is spaced from the maximum opening plane E_(Max) and is substantially arranged and/or displaced in the closing direction SR of the propeller blade 14. The opening direction OR and the closing direction SR correspond substantially to arc-shaped pivot movements of the propeller blade 14 when it is pivoted about the pivot axis S. The stop apparatus 18 is configured so that the center of mass MSP in the maximum open position P2 is spaced, in the closing direction SR, from the maximum opening plane E_(Max).

The propeller blade 14 has a first, distally arranged propeller blade portion 14 a and a second, proximally arranged propeller blade portion 14 b wherein the first propeller blade portion 14 a is offset relative to the second propeller blade portion 14 b substantially in the closing direction SR.

Accordingly, an advantageous spacing of the center of mass MSP in the closing direction SR in relation to the maximum opening plane E_(Max) is achieved or increased. The center of mass MSP represents an effective force application point EAP of a centrifugal force that is suitable for generating an opening moment (see FIG. 2a, b ).

Furthermore, the propeller blade 14 has a propeller blade tip portion 144, a propeller blade shaft portion 146 and a propeller blade root portion 148. In the embodiment shown in FIG. 1, the propeller blade tip portion 144 is connected to the propeller blade shaft portion 146 form-fittingly and frictionally and together they form the first propeller blade portion 14 a, whereas the propeller blade root portion 148 forms the second propeller blade portion 14 b. The first and second propeller blade portions 14 a and 14 b are firmly connected to one another so that a transmission of the propeller thrust forces is assured.

The propeller blade tip portion 144 has an additional body 142 which forms a propeller blade tip 19. In the present example, the additional body 142 is formed integrally with the propeller blade tip portion 144. The additional body 142 can be present in the form of an uplift body 142 a, for example, in the form of a winglet 13 (see FIG. 5). The uplift body 142 a can be configured such that, when the folding propeller 10 is driven, it experiences a dynamic uplift which is applied to the center of pressure DP of the uplift body 142 a. The center of pressure DP thus represents an effective force application point EAP of the dynamic uplift that is suitable for generating an opening moment (see FIG. 5).

In the embodiment shown, due to the offset described above of the first propeller blade portion 14 a relative to the second propeller blade portion 14 b in the closing direction SR, an advantageous spacing of the center of pressure DP in the closing direction SR relative to the maximum opening plane E_(Max) is also achieved or increased.

In the regions in which different propeller roots 15 can make contact with one another or can overlap one another, the propeller roots 15 of the two propeller blades 14 have spur gear toothing (not shown). This enables an interlocking of the propeller blades 14 and thus a synchronization of the pivot movements of the propeller blades 14.

Furthermore, in the embodiment shown, the propeller blade 14 is configured such that the center of mass MSP is arranged distally in relation to the centroid VSP of the propeller blade 14. In other words, the material density in the distal region of the propeller blade 14 is greater than in the proximal region. This is achieved, for example, in that the additional body 142 is present in the form of a mass body 142 b (see FIGS. 3a and 3c ). For example, the mass body 142 b and/or the propeller blade tip portion 144 may thus be formed of metal. In general, the additional body 142 and/or the propeller blade tip portion 144 can be made of a material of higher density than the remainder of the propeller blade portions (for example, the propeller blade shaft portion 146 and propeller blade root portion 148). In the embodiment shown, the propeller blade shaft portion 146 consists of plastics.

The embodiment described above has the advantage that the folding propeller can be configured particularly weight-optimized, whereas the desired centrifugal force can be influenced by an arrangement of the center of mass as far distally as possible.

Additionally, the hub 12 is formed of plastics. This reduces the moment of inertia of the hub 12 and the hub 12 can be constructed with a larger diameter. By this means, the pivot axis S defined by the mounting apparatus 16 can be arranged with a greater spacing h (see FIG. 2) from the rotation axis D. This has the result that, in an opened pivot position of the propeller blade 14, the center of mass MSP and the center of pressure DP have a greater spacing from the rotation axis D, which in turn leads to an increase in the desired opening forces.

In the description of the following drawings, the relevant forces and moments will be considered, inter alia.

FIG. 2a shows a schematic plan view of the folding propeller 10 of FIG. 1, wherein a single propeller blade 14 is shown in two different pivot positions, specifically the maximum closed position P1 and a middle open position Pm. Starting from the maximum closed position P1, due to the rotation of the hub 12 about its rotation axis D, a centrifugal force F_(centrifugal,1) acts upon the center of mass MSP which is spaced at a distance r_(centrifugal,1) (not shown) from the rotation axis D, wherein the centrifugal force F_(centrifugal,1) is directed radially outwardly, i.e. in the direction of a normal (not shown) extending through the center of mass MSP to the rotation axis D. The centrifugal force F_(centrifugal,1) has an opening force component F_(centrifugal,lever,1) which is applied to the center of mass MSP and is directed perpendicularly to a lever with the length of the spacing a_(MSP-S) from the center of mass MSP to the pivot axis S. The opening force component F_(centrifugal,lever,1) thus generates, via said lever, an opening moment M_(opening,1) (not shown). By this means, the center of mass MSP, disregarding the translational travel motion of the boat, is accelerated tangentially relative to the pivot axis S and is thus pivoted out of the maximum closed position P1.

The relationship just described applies for both possible rotations DR of the hub 12, that is, for forward travel and rearward travel of the boat.

As a result, the propeller blade 14 pivots in the opening direction OR, wherein the representation of the middle open position Pm in FIG. 2a makes clear that with increasing spacing r_(centrifugal,m) of the center of mass MSP from the rotation axis D, the centrifugal force F_(centrifugal,m) has also increased in relation to F_(centrifugal,1). F_(centrifugal,m) can be determined as follows:

F _(centrifugal,m) =m*ω ² *r _(centrifugal,m),

where m=mass of the propeller blade 14, ω=angular velocity of the hub rotation and

r _(centrifugal,m)=pivot axis spacing h+a _(MSP-S)*cos(α_(m));

wherein h=spacing of pivot axis S from rotation axis D, and α_(m)=opening angle in the middle pivot position.

In general, the opening angle α represents the angle between the maximum opening plane E_(Max) and the lever, i.e. the distance from the center of mass MSP to the pivot axis S.

FIG. 2b shows a continuation of the pivot movement of FIG. 2a , wherein the propeller blade 14 is pivoted into the maximum open position P2.

In particular, in this maximum open position P2, an opening force component F_(centrifugal,lever,2) acts upon the center of mass MSP and generates an opening moment M_(opening,2) as described above. Therein, M_(opening,2) and F_(centrifugal,lever,2) can be determined as follows:

M _(opening,2) =F _(centrifugal,lever1,2) *a _(MSP-S)

where F _(centrifugal,lever,2) =F _(centrifugal,2)*sin(α₂)

The opening force F_(centrifugal,lever,2) thereby presses the propeller blade 14 against the stop apparatus 18. In addition, the opening moment M_(opening) is greater than a closing moment M_(close) (not shown) acting overall simultaneously. This applies, in particular, for the rearward drive and the braking.

FIG. 3a shows a schematic front view of a folding propeller blade 14 of a folding propeller 10 according to a further embodiment. The additional body 142 can be configured as a mass body 142 b, for example, as a cylinder (see FIG. 3c ), in some embodiments as a curved cylinder or as an uplift body 142 a (see FIG. 3b ) or in another suitable form. The propeller blade tip portion 144 is therein in some embodiments formed integrally with the additional body 142. Furthermore, the propeller blade tip portion 144 may be formed of metal.

In some embodiments, the propeller blade tip portion 144 is connected form-fittingly or frictionally to the propeller blade shaft portion 146. As shown dashed in FIG. 3a , the propeller blade tip portion 144 has a tongue 1440 which is cast into the propeller blade shaft portion 146 and/or is connected to the propeller blade shaft portion 146 via a screw connection or a rivet connection or another suitable connection. Furthermore, the propeller blade shaft portion 146 is in some embodiments formed of plastics.

The tongue 1440 is in some embodiments formed integrally with the propeller blade tip portion 144. The tongue 1440 can be configured such that the propeller blade tip portion 144 has a stepped form from a separation edge 145 in the proximal direction (see FIG. 3b, 3c ), in order to be received in a corresponding distally oriented recess in the propeller blade shaft portion 146.

In order to configure the possible connection interfaces of additional bodies 142 to the propeller blade 14 or from the propeller blade tip portion 144 to the propeller blade shaft portion 146, a person skilled in the art would accordingly take account of the radii R1 and R2 shown in FIG. 3 a.

FIGS. 3b and 3c show, in a schematic side view, a further embodiment of the propeller blade tip portion 144. It has an additional body 142 which in FIG. 3b is present in the form of a uplift body 142 a and is inclined in the rearward travel direction. Such an inclination of the uplift body 142 a can be used to generate dynamic uplift (see FIG. 5). In FIG. 3c , the additional body 142 is present as a mass body 142 b, in this case in the form of a curved cylinder with the curvature of radius R2 (see FIG. 3a ). The mass body 142 b can be used for increasing the centrifugal force. The tongue 1440 serves for the aforementioned connection of the propeller blade tip portion 144 to the propeller blade shaft portion 146.

The separation edge 145 can be used for the design or for improving the connection of the aforementioned propeller blade portions.

FIG. 3d, 3e show schematic frontal views and cross-sections of the tongue 1440 of the propeller blade tip portion 144 which serves for the form-fitting and/or frictional connection to the propeller blade shaft portion 146. In FIG. 3d , the tongue 1440 has bores 1442 which can serve in the aforementioned connection, for example, as through holes or threaded holes for a screw connection, bolt connection or rivet connection. In FIG. 3e , by contrast, the tongue 1440 has webs 1444 which can advantageously be used in the aforementioned connection, for example, for the aforementioned injection molding or casting connection.

As shown in FIGS. 3a, 3d and 3e , the tongue 1440 can be trapezoid or rectangular, but can also have any other shape suitable for the connection described.

FIG. 4 shows a schematic front view of a plastics propeller blade 14 with a metal inlay 20 according to a further embodiment of the folding propeller 10. Herein, the metal inlay 20 is embedded in the plastics propeller blade 14. For example, the metal inlay 20 can be cast into the plastics propeller blade 14. In this way, advantages are achieved with regard to corrosion and servicing, while due to the metal inlay 20, the arrangement of the center of mass MSP and a sufficient stiffness of the plastics propeller blade 14 can be ensured. The embodiment shown in FIG. 4 can have, in particular, the previously and subsequently described features, for example, an additional body 142, even if this is not explicitly shown in FIG. 4.

FIG. 5 shows a schematic plan view of a further embodiment of a propeller blade 14 of the folding propeller 10 in the maximum closed position P2. In this example, the propeller blade 14 has an uplift body 142 a in the form of a winglet 13. The winglet 13 has, in its cross-section (see FIG. 6), an airfoil profile with a correspondingly formed winglet upper side 13 a and winglet underside 13 b. Furthermore, the winglet 13 has a first, distal portion 131 and a second, proximal portion 132 wherein the latter is suitably equipped, in particular, for connecting to the remainder of the propeller blade 14. The winglet longitudinal axis L_(W) is inclined relative to the remainder of the propeller blade 14 in the closing direction SR, in particular, inclined by the angle β relative to the longitudinal axis L_(shaft) of the propeller blade shaft portion 146. The winglet 13 is configured (see FIG. 6) such that, in particular, when surrounding water flows over the winglet 13, a dynamic uplift force F_(uplift) acts upon the winglet and, associated therewith, an openingly acting uplift force component F_(uplift,lever) acts upon the propeller blade 14. F_(uplift,lever) is the component of the uplift force F_(uplift) which generates an opening moment M_(uplift,opening) that acts perpendicularly via a lever to the pivot axis on the propeller blade 14.

Shown schematically in FIG. 5 is an effective application point EAP of the uplift force F_(uplift) acting overall upon the winglet 13 in the form of a projection of the center of pressure DP of the winglet profile. Accordingly, the relevant lever results from the spacing of the center of pressure DP from the pivot axis S, that is the distance app-s. In the design of the folding propeller 10, a person skilled in the art can thus easily create a model to describe the moment M_(uplift,opening) which acts openingly due to the uplift and which comprises the parameters shown in FIG. 5. A person skilled in the art can thus determine, for a given configuration, an advantageous winglet inclination angle β. The winglet 13 is configured such that the effective force application point EAP of the uplift force F_(uplift) is clearly spaced from the maximum opening plane E_(Max) and is offset in the closing direction SR.

The arrangement shown in FIG. 5 of the winglet 13 in relation to the propeller blade shaft portion 146 is geometrically simple and here is substantially described by means of the two longitudinal axes L_(W) and L_(shaft) and their inclination angle β to one another. However, the winglet arrangement can deviate therefrom substantially. Alternatively, the winglet 13 can be configured elliptical or annular, for example, as a spiroid or a split-wing loop. Furthermore, the winglet 13 can have a plurality of portions and therefore a plurality of portion longitudinal axes (for example, a T-shape or a Y-shape) and can accordingly be arranged on the propeller blade shaft portion 146 or on the propeller blade 14.

FIG. 6 shows schematically an exemplary profile in a section A-A of the winglet 13 of FIG. 5. In some embodiments, the winglet profile is configured as a normal profile, wherein the winglet upper side 13 a is configured convex and the winglet underside 13 b is configured s-shaped. If a normal profile is used, this can in some embodiments be oriented toward the folding propeller 10 such that during rearward drive, the flow of the surrounding water, represented here as the flow AS, and thus the dynamic uplift, is particularly advantageously used. A reinforcement of the opening moment M_(opening) is particularly preferred for rearward drive. Alternatively, the winglet profile can be configured as a symmetrical profile or can have any further advantageous, uplift-generating profile shape. As shown by way of example in FIG. 6, the surrounding water flows faster on the upper side 13 a than on the underside 13 b, so that the dynamic uplift force F_(uplift) acts upon the winglet 13, is applied to the center of pressure DP or the effective force application point EAP and is directed perpendicularly to the flow AS and away from the winglet upper side 13 a.

FIG. 7 shows a schematic perspective view of the winglet 13 according to one embodiment. In this example, the winglet 13 is formed integrally. In this way, by simple design means, a hydrodynamically optimized propeller blade can be provided.

FIG. 8 shows a perspective schematic view of a water vehicle 100 during rearward drive with a folding propeller 10 according to a further embodiment. The folding propeller 10 comprises a hub 12 and two identical propeller blades 14. The propeller blade 14 is attached in the region of its propeller root (not shown) via a mounting apparatus (not shown) to the hub 12. The hub 12 is rotatable about a rotation axis D and is drivable via a boat drive shaft (not shown) to which it is connected for conjoint rotation. The mounting apparatus (not shown) defines a propeller blade pivot axis S which is arranged perpendicularly to the rotation axis D. The propeller blade 14 is pivotable about the propeller blade pivot axis S between a maximum closed position (not shown) and a maximum open position P2. In a contact region of the propeller root (not shown) and the hub 12, the folding propeller 10 has a propeller blade stop apparatus (not shown) which limits the opening of the propeller blade 14 and thus defines the maximum open position P2.

The propeller blade 14 is configured as an airfoil which means that, on rotation of the hub 12 in the rotation direction DR or contrary to the rotation direction DR, it undergoes uplift forces through the displacement of the surrounding water and transmits said forces in the form of a resultant thrust via the hub 12 to the drive.

In the propeller blade tip portion 144, a reversal element 143 is arranged to be pivotable about a reversal element pivot axis S_(U) which is substantially parallel to the propeller blade longitudinal axis L_(P). The propeller blade 14 has a front edge 150 and a rear edge 151.

In FIG. 8, the hub 12 is rotated in the rotation direction DR which corresponds to a rearward drive, so that due to the linear velocity v_(linear), a flow AS impacts upon the propeller blade rear edge 151. The flow AS presses against the reversal element 143, which pivots or is pivoted accordingly in the direction of the maximum folded-out position U2. The stream AS henceforth impinging upon the reversal element 143 brings about the reversed force F_(reverse) which acts via an effective force application point EAP on the propeller blade 14 and via a lever of length a_(U-S) to the propeller blade pivot axis S, generates an opening moment M_(opening,reverse).

By means of the rotation of the hub 12 in the rotation direction DR, the propeller blade 14 experiences uplift forces F_(uplift,rearward) directed in the rearward direction of travel, the sum of which results in a thrust F_(thrust,rearward) directed in the rearward direction of travel. In addition, the uplift forces F_(uplift,rearward) cause a moment (not shown) having a closing effect on the propeller blade 14, the lever of which is significantly smaller, substantially half as great as the lever a_(U-S) of the previously described openingly acting moment M_(opening,reverse).

In the design of the folding propeller 10, on the basis of the arrangement disclosed, a person skilled in the art can thus easily create a model to quantify the openingly and closingly acting moments, comprising the elements and parameters shown in FIG. 8. A skilled person can therefore, for example, configure the propeller blade 14 and the reversal element 143 such that a desired opening moment for particular parameter configurations results.

FIG. 9a shows a schematic front view and FIG. 9b the corresponding side view of the propeller blade 14 shown in FIG. 8 during rearward drive of the folding propeller 10. In the example shown, the reversal element 143 is arranged in the propeller blade tip region, that is, at the distal end of the propeller blade 14. Through the rotation of the propeller blade 14, the reversal element 143 moves with the linear velocity about the rotation axis. Thereby, a flow AS lies continuously against the reversal element 143. Thereby, an uplift results which generates the reversed force F_(reverse) which acts upon the reversal element 143 and pivots the reversal element 143 about its pivot axis S_(U) into its maximum folded-out position U2. This pivoting is limited by a stop apparatus (not shown) which therefore defines the maximum folded-out position U2. Furthermore, a transmission apparatus (not shown) is provided on the propeller blade 14 in the region of the reversal element 143, which is configured to transmit the reversed force F_(reverse) engaging upon the reversal element 143 to the propeller blade 14, so that F_(reverse)—as described in relation to FIG. 8—generates via the lever a_(U-S) to the propeller blade pivot axis S, the opening moment M_(opening,reverse). The stop apparatus can therein be configured integrally with the transmission apparatus. In particular, the transmission apparatus can be configured to transmit the reversed force F_(reverse) applied to the reversal element 143 via suitable elements to the propeller blade 14 by means of compression forces and/or tensile forces.

As FIG. 9b shows, the reversal element 143 can have a form in its distal end region which is suitable to catch the flow AS during rearward drive such that the reversal element 143 is pivoted out of a maximum folded-in position (see FIG. 10a, b ) automatically or autonomously in the direction of its maximum folded-out position 143.

FIG. 10a shows a schematic front view and FIG. 10b the corresponding side view of the propeller blade 14 shown in FIG. 8 during forward drive of the folding propeller 10. Due to the flow AS against the propeller blade front edge 150, the reversal element 143 remains substantially in its maximum folded-in position U1. If braking is carried out during forward travel, the vector of the linear velocity V_(linear,forward) rotates accordingly into the opposite direction and consequently also the flow AS. By this means, the reversal element 143 is pivoted into the maximum folded-out position U2, so that, as described above, the reversal element 143 can provide a moment acting closingly on the propeller blade 14.

As far as practicable, all the individual features which are described in the exemplary embodiments can be combined with one another and/or exchanged without departing from the scope of the present disclosure.

REFERENCE SIGNS

-   -   10 Folding propeller     -   12 Hub     -   13 Winglet     -   13 a Winglet upper side     -   13 b Winglet underside     -   14 Propeller blade     -   14 a First, distal propeller blade portion     -   14 b Second, proximal propeller blade portion     -   15 Propeller root     -   16 Mounting apparatus     -   18 Stop apparatus     -   19 Propeller blade tip     -   20 Metal inlay     -   100 Water vehicle     -   131 First, distal winglet portion     -   132 Second, proximal winglet portion     -   142 Additional body     -   142 a Uplift body     -   142 b Mass body     -   143 Reversal element     -   144 Propeller blade tip portion     -   145 Separation edge     -   146 Propeller blade shaft portion     -   148 Propeller blade root portion     -   150 Propeller blade front edge     -   151 Propeller blade rear edge     -   1440 Tongue     -   1442 Bore     -   1444 Web     -   a_(MSP-S) Spacing/distance center of mass MSP to pivot axis S     -   a_(DP-S) Spacing/distance center of pressure DP to pivot axis S     -   AS Flow     -   D Rotation axis     -   DP Center of pressure     -   EAP Effective force application point     -   E_(Max) Maximum opening plane     -   F_(uplift) Uplift force     -   F_(centrifugal) Centrifugal force     -   F_(reverse) Reversed force on the reversal element     -   h Spacing rotation axis D to pivot axis S     -   L_(P) Propeller blade longitudinal axis     -   L_(shaft) Longitudinal axis of propeller blade shaft portion     -   L_(W) Winglet longitudinal axis     -   M_(opening) Opening moment     -   M_(closing) Closing moment     -   MSP Center of mass of propeller blade     -   N_(D) Normal to the rotation axis D     -   OR Opening direction     -   P1 Maximum closed position of the propeller blade/folding         propeller     -   Pm Middle open position of the propeller blade/folding propeller     -   P2 Maximum open position of the propeller blade/folding         propeller     -   r_(centrifugal) Spacing rotation axis D to center of mass MSP         (radius of centrifugal force)     -   R1 Outer radius of propeller blade shaft portion     -   R2 Outer radius of folding propeller or curvature of cylinder     -   S Pivot axis     -   S_(U) Pivot axis of reversal element     -   SR Closing direction     -   U1 Maximum folded-in position of reversal element     -   U2 Maximum folded-out position of reversal element     -   α Opening angle of propeller blade/angle between a_(MSP-S) and         E_(max)     -   β Inclination angle of winglet/angle between L_(w) and L_(shaft) 

1. A folding propeller for a water vehicle, the folding propeller comprising: a hub drivable about a rotation axis via a drive shaft, and a propeller blade arranged on the hub to be pivotable about a pivot axis between a maximum closed position and a maximum open position, wherein the pivot axis defines, together with a normal to the rotation axis which intersects the pivot axis, a maximum opening plane, wherein in a driven state and a pivot position of the propeller blade in a region of the maximum open position, an opening force acts upon the propeller blade which results from rotation of the folding propeller and in relation to the rotation axis is directed substantially radially outwardly, wherein an effective force application point of the opening force is arranged spaced from the maximum opening plane and is substantially arranged in a closing direction of the propeller blade.
 2. The folding propeller according to claim 1, wherein the effective force application point of the opening force corresponds to a center of mass of the propeller blade, wherein one or both of the opening force is a centrifugal force or the effective force application point of the opening force corresponds to the center of pressure of an uplift body arranged on the propeller blade, wherein the opening force is an uplift force.
 3. The folding propeller according to claim 1, wherein the folding propeller has a stop apparatus which defines the maximum open position of the propeller blade and the effective force application point of the opening force is arranged outside the maximum opening plane in the closing direction such that in the maximum open position of the propeller blade, an opening moment acts which presses the propeller blade against the stop apparatus.
 4. The folding propeller according to claim 1, wherein the propeller blade has an additional body that is one or both of configured as an uplift body or configured as a mass body, wherein the uplift body is configured as a winglet and the mass body has a curved cylinder.
 5. The folding propeller according to claim 1, wherein the propeller blade has a first propeller blade portion that is distally arranged, and a second propeller blade portion that is proximally arranged, wherein the first propeller blade portion is offset relative to the second propeller blade portion substantially in the closing direction.
 6. The folding propeller according to claim 1, wherein the propeller blade has a propeller blade tip portion, a propeller blade shaft portion and a propeller blade root portion, wherein the propeller blade shaft portion is arranged between the propeller blade tip portion and the propeller blade root portion, and wherein one or both of the propeller blade shaft portion or the propeller blade tip portion is offset relative to the propeller blade root portion substantially in the closing direction of the propeller blade.
 7. The folding propeller according to claim 6, wherein the propeller blade is configured such that a center of mass of the propeller blade is arranged distally in relation to a centroid of the propeller blade, wherein the center of mass of the propeller blade is arranged either in the propeller blade tip portion or in the propeller blade shaft portion.
 8. The folding propeller according to claim 1, wherein the propeller blade has a propeller root, wherein the propeller root has a mounting apparatus for attaching the propeller blade to the hub and the mounting apparatus defines the pivot axis.
 9. The folding propeller according to claim 6, wherein the propeller blade has an additional body that is configured as one or more of an uplift body or as a mass body, wherein one or both of the propeller blade tip portion or the additional body is formed of metal.
 10. The folding propeller according to claim 9, wherein the propeller blade or the propeller blade tip portion is configured integrally with the additional body.
 11. The folding propeller according to claim 6, wherein one or both of the propeller blade shaft portion or the hub is formed at least partially of plastics.
 12. The folding propeller according to claim 6, wherein the propeller blade tip portion is one or both of connected form-fittingly or frictionally to the propeller blade shaft portion.
 13. The folding propeller according to claim 6, wherein the propeller blade tip portion has a tongue which is one or both of cast into the propeller blade shaft portion or is connected to the propeller blade shaft portion via a releasable connection, in particular a screw connection.
 14. The folding propeller according to claim 1, wherein a metal insert is embedded in the propeller blade.
 15. A folding propeller for a water vehicle, the folding propeller comprising: a hub drivable about a rotation axis via a drive shaft, and a propeller blade arranged on the hub to be pivotable about a pivot axis, wherein the propeller blade has a reversal element, which is configured such that during rearward drive, a reversed force acts upon the reversal element and is directed substantially perpendicularly to a propeller blade longitudinal axis in an opening direction of the propeller blade.
 16. The folding propeller according to claim 15, wherein the reversal element is arranged in a propeller blade tip portion.
 17. The folding propeller according to claim 15, wherein the reversal element is arranged on the propeller blade to be pivotable about the pivot axis which is substantially parallel to the propeller blade longitudinal axis.
 18. The folding propeller according to claim 15, wherein the reversal element is pivotable between a maximum folded-in position and a maximum folded-out position, wherein the reversal element assumes a maximum folded-in position when the folding propeller is in forward drive, wherein in the maximum folded-in position, the reversal element is oriented substantially aligned with the propeller blade, wherein the reversal element assumes the maximum folded-out position when the folding propeller is in rearward drive, wherein in the maximum folded-out position, the reversal element experiences the reversed force.
 19. The folding propeller according to claim 15, wherein the reversed force generates an opening moment on the propeller blade via a lever to the pivot axis.
 20. A drive for a water vehicle having a folding propeller comprising: a hub which is drivable about a rotation axis via a drive shaft, and a propeller blade which is arranged on the hub to be pivotable about a pivot axis between a maximum closed position and a maximum open position, wherein the pivot axis defines, together with a normal to the rotation axis which intersects the pivot axis, a maximum opening plane, wherein in a driven state and a pivot position of the propeller blade in a region of the maximum open position, an opening force acts upon the propeller blade which results from rotation of the folding propeller and in relation to the rotation axis is directed substantially radially outwardly, wherein an effective force application point of the opening force is arranged spaced from the maximum opening plane and is substantially arranged in a closing direction of the propeller blade.
 21. A drive for a water vehicle having a folding propeller comprising: a hub drivable about a rotation axis via a drive shaft, and a propeller blade arranged on the hub to be pivotable about a pivot axis, wherein the propeller blade has a reversal element, which is configured such that during rearward drive, a reversed force-acts upon the reversal element and is directed substantially perpendicularly to a propeller blade longitudinal axis in an opening direction of the propeller blade. 